Excerpt

Immune stress is induced by exogenous microbe attacking the animal body, such as bacterial infection and vaccination, which is manifested as the changes of body metabolism and the inflammation (Klasing et al., 1987). In animal experiment, lipopolysaccharide (LPS) is used to induce immune stress model (Xie et al., 2000), which is an important component of the cell wall of Gram‐negative bacteria and could stimulate animals to produce inborn immune to change the nutrient metabolism, which reduces the daily feed intake and average daily weight gain, and lowers feed conversion ratio, resulting in negative growth performance (Liu et al., 2014). Therefore, it is important to avoid immune stress. In daily management, the growth inhibition and body catabolism caused by immune stress can be relieved through feeding antibiotics (Roura et al., 1992). On the other hand, balanced nutrition is also important to alleviating the productivity degradation due to immune stress (Takahashi et al., 2002).Artemisia argyi aqueous extract (AAE) is isolated from A. argyi, a Chinese mugwort, which is a traditional herbal medicine. Chinese mugwort contains many kinds of bioactive chemicals such as polysaccharides, flavonoids, essential oil and triterpenoids (Zhang et al., 2013), and some vitro cell culture tests and antibacterial experiments have proved that mugwort possesses many biological activities such as antibacterial, antitumour, antioxidant and immunomodulatory activity (Guan et al., 2006; Lan et al., 2010; Bao et al., 2013; Zhang et al., 2014). In recent years, mugwort has been used as a feed additive to promote blood circulation, enhance the body metabolism and improve feed conversion rate and production performance (Khalaji et al., 2011; Kim et al., 2012). However, it is unclear how mugwort promotes the growth performance of broilers. Based on previous studies, the present experiment was conducted to investigate the effect of AAE on broiler chickens under immune stress, to identify the growth‐promoting mechanism of mugwort.